Fine
calcium hypophosphite can be synthesized by sodium hypophosphite
and calcium chloride via the replacement reaction, and sodium hypophosphite
can be synthesized from phosphorus via the intermediate of Ca(H2PO2)2. Both processes involve the interactive
quaternary system of (Ca2+ + Na+)//(Cl– + (H2PO2)− + H2O) and its subsystems. In this study, the (solid + liquid) phase
diagrams of the (Ca(H2PO2)2 + H2O) binary system from freezing to boiling point at normal
pressure, and (Ca(H2PO2)2 + CaCl2 + H2O), (Ca(H2PO2)2 + NaH2PO2 + H2O) ternary systems
at 273.15 K were experimentally determined via the classical isothermal
solubility equilibrium method. It was found that (1) one anhydrous
salt of Ca(H2PO2)2 occurs in (Ca(H2PO2)2 + H2O) binary systems
with temperatures ranging from freezing to boiling points, (2) two
solid salts of Ca(H2PO2)2 and CaCl2·6H2O exist in the (Ca(H2PO2)2 + CaCl2 + H2O) system,
and (3) Ca(H2PO2)2, NaH2PO2·H2O and one incompatible double salt
of NaCa(H2PO2)3 exist in the (Ca(H2PO2)2 + NaH2PO2 + H2O) system, and NaCa(H2PO2)3 has very low solubility and occupies a large solid field
in the ternary system.
The thermodynamics phase equilibria
of the aqueous ternary systems
(Mg(H2PO2)2 + NaH2PO2 + H2O) and (Mg(H2PO2)2 + MgCl2 + H2O) at 323.15K were investigated
via the classical isothermal solubility equilibrium method. The solubilities
and densities of the equilibrated solution were determined. The species
of solid phase were confirmed by using the Scherinemakers’
wet residue method and with the aid of X-ray powder diffraction testing.
In accordance with the experimental data, the phase diagrams and density
versus composition diagrams were constructed. Both ternary systems
are of complex type with three-species solid-salts of [Na(H2PO2)2·H2O, Mg(H2PO2)2·6H2O, and double-salt
NaMg(H2PO2)3], and four-species solid-salts
of [hydrate Mg(H2PO2)2·6H2O, MgCl2·6H2O, dehydrate Mg(H2PO2)2, and double-salt species Mg2(H2PO2)2Cl2·6H2O] formed respectively in the corresponding system. The solubility
of Mg(H2PO2)2 is very low in Na(H2PO2)2 aqueous solution but large in
MgCl2 aqueous solution. Mg(H2PO2)2·6H2O will dehydrate and transform into Mg(H2PO2)2 in the concentrated MgCl2 aqueous solution.
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